The disclosure relates generally to distributed communications systems (DCSs), such as distributed antenna systems (DAS) for example, capable of distributing wireless radio-frequency (RF) communications services over wired communications mediums to remote units to provide remote communications coverage areas for distributing the RF communications services to wireless client devices.
Wireless customers are increasingly demanding wireless communications services, such as cellular communications services and Wi-Fi services. Thus, small cells, and more recently Wi-Fi services, are being deployed indoors. At the same time, some wireless customers use their wireless communication devices in areas that are poorly serviced by conventional cellular networks, such as inside certain buildings or areas where there is little cellular coverage. One response to the intersection of these two concerns has been the use of wireless distributed communications systems (DCSs), such as distributed antenna systems (DASs). DASs include remote antenna units (RAUs) configured to receive and transmit communications signals to client devices within the antenna range of the RAUs. DASs can be particularly useful when deployed inside buildings or other indoor environments where the wireless communication devices may not otherwise be able to effectively receive radio frequency (RF) signals from a source.
In this regard, FIG. 1 illustrates a wireless DCS 100 that is configured to distribute communications services to remote coverage areas 102(1)-102(N), where ‘N’ is the number of remote coverage areas. The wireless DCS 100 in FIG. 1 is provided in the form of a DAS 104. The DAS 104 can be configured to support a variety of communications services that can include cellular communications services, wireless communications services, such as RF identification (RFID) tracking, Wireless Fidelity (Wi-Fi), local area network (LAN), and wireless LAN (WLAN), wireless solutions (Bluetooth, Wi-Fi Global Positioning System (GPS) signal-based, and others) for location-based services, and combinations thereof, as examples. The remote coverage areas 102(1)-102(N) are created by and centered on remote units 106(1)-106(N) communicatively coupled to a central unit 108 (e.g., a head-end controller, a central unit, or a head-end unit). The central unit 108 may be communicatively coupled to a source transceiver 110, such as for example, a base transceiver station (BTS) or a baseband unit (BBU). In this regard, the central unit 108 receives downlink communications signals 112D from the source transceiver 110 to be distributed to the remote units 106(1)-106(N). The downlink communications signals 112D can include data communications signals and/or communication signaling signals, as examples. The central unit 108 is configured with filtering circuits and/or other signal processing circuits that are configured to support a specific number of communications services in a particular frequency bandwidth (i.e., frequency communications bands). The downlink communications signals 112D are communicated by the central unit 108 over a communications link 114 over their frequency to the remote units 106(1)-106(N).
With continuing reference to FIG. 1, the remote units 106(1)-106(N) are configured to receive the downlink communications signals 112D from the central unit 108 over respective communications links 114(1)-114(N). The downlink communications signals 112D are configured to be distributed to the respective remote coverage areas 102(1)-102(N) of the remote units 106(1)-106(N). The remote units 106(1)-106(N) are also configured with filters and other signal processing circuits that are configured to support all or a subset of the specific communications services (i.e., frequency communications bands) supported by the central unit 108. In a non-limiting example, the communications links 114(1)-114(N) may be a wired communications link, a wireless communications link, or an optical fiber-based communications link. Each of the remote units 106(1)-106(N) may include an RF transmitter/receiver 116(1)-116(N) and a respective antenna 118(1)-118(N) operably connected to the RF transmitter/receiver 116(1)-116(N) to wirelessly distribute the communications services to a wireless client device 120 within the respective remote coverage areas 102(1)-102(N). The remote units 106(1)-106(N) are also configured to receive uplink communications signals 112U from the wireless client device 120 in the respective remote coverage areas 102(1)-102(N) to be distributed to the source transceiver 110.
One problem that can exist with wireless communication systems, including the system 100 in FIG. 1, is the multi-path (fading) nature of signal propagation. This simply means that local maxima and minima of desired signals can exist over a picocell coverage area. A receiver antenna located at a maximum location will have better performance or signal-to-noise ratio (SNR) than a receiver antenna located in a minimum position. Signal processing techniques can be employed to improve the SNR of wireless data transmission in such wireless communication systems. For example, spatial diversity can be utilized in instances involving many access points. Other signal processing techniques include multiple-input, multiple-output (MIMO) techniques for increasing bit rates or beam forming for SNR, or wireless distance improvement. MIMO is the use of multiple antennas at both a transmitter and receiver to increase data throughput and link range without additional bandwidth or increased transmit power. MIMO technology can be employed in DASs to increase the bandwidth up to twice the nominal bandwidth.
Even with the potential doubling of bandwidth in a DCS employing MIMO technology, a client device must still be within range of two MIMO antennas to realize the full benefits of increased bandwidth of MIMO technology. Ensuring uniform MIMO coverage may be particularly important for newer cellular standards, such as Long Term Evolution (LTE), where increased bandwidth requirements are expected by users of client devices in all coverage areas.
MIMO communications services require at least two (2) communications streams being distributed in a given coverage area. For example, to provide MIMO communications services in the DAS 104 in FIG. 1, remote units 106(1)-106(N) in the DAS 104 can be co-located. For example, FIG. 2 illustrates the DAS 104 in FIG. 1 with co-located remote units 106(1), 106(2) and co-located remote units 106(3), 106(4). The co-located remote units 106(1), 106(2) are separated a distance D1 from the other co-located remote units 106(3), 106(4) such that two distinct MIMO coverage areas 204(1), 204(2) are formed by the respective co-located remote units 106(1), 106(2) and co-located remote units 106(3), 106(4). Each remote unit 106(1)-106(4) has a respective radio 202(1)-202(4) configured to distribute a communication stream including one or more communications bands. Each radio 202(1)-202(4) may be configured to support the same communications bands, or a common subset of communications bands. Co-located remote units 106(1), 106(2) provide the first MIMO coverage area 204(1) by respectively receiving and distributing MIMO communications streams 200(1), 200(2). Co-located remote units 106(3), 106(4) provide the second MIMO coverage area 204(2) by also respectively receiving and distributing MIMO communications streams 200(1), 200(2). As shown in FIG. 2, a wireless client device 120 located within the first MIMO coverage area 204(1) will receive the MIMO communications streams 200(1), 200(2) for a MIMO communications service from the co-located remote units 106(1), 106(2), because the wireless client device 120 will be in communications range of both remote units 106(1), 106(2). Similarly, if the wireless client device 120 were located in the second MIMO coverage area 204(2) in range of both remote units 106(3), 106(4), the wireless client device 120 would receive MIMO communications streams 200(1), 200(2) for a MIMO communications service through remote units 106(3), 106(4). If however, the wireless client device 120 were located in a coverage area outside or on the edge of the first and second MIMO coverage areas 204(1), 204(2), the wireless client device 120 may still be in communication range of at least one of the remote units 106(1)-106(4) to receive one of the MIMO communications streams 200(1) or 200(2). However, the wireless client device 120 may not be in communication range with sufficient signal-to-noise (SNR) ratio of another remote unit 106(1)-106(4), to receive the other MIMO communications streams 200(2) or 200(1). Thus, in this example, the wireless client device 120 would only receive single input, single output (SISO) communications services in the DAS 104.
Providing co-located remote units 106(1)-106(N) in the DAS 104 can increase the MIMO coverage areas 204 provided in the DAS 104 to reduce or eliminate non-MIMO coverage areas where only SISO communications services are available. However, providing co-located remote units 106(1)-106(N) increases the number of remote units 106(1)-106(N) in the DAS 104 for the number of MIMO coverage areas 204 provided. For example, as shown in FIG. 2, two (2) remote units 106(1), 106(2) are required to be co-located to form the single MIMO coverage area 204(1). If a 4×4 MIMO communications service is desired, then four (4) remote units 106(1)-106(N) would be required to be co-located to form a single MIMO coverage area 204. Providing an increased number of remote units 106(1)-106(N) to provide MIMO communications services in the DAS 104 adds complexity and associated cost by requiring support of a greater number of remote units 106(1)-106(N) to as well as increased costs associated with providing additional communications links 114(1)-114(N) for each MIMO coverage area 204.
No admission is made that any reference cited herein constitutes prior art. Applicant expressly reserves the right to challenge the accuracy and pertinency of any cited documents.